I'm pretty sure that merely tab-switching hasn't fixed it for me. I've done both mouse and alt-tab, i've ctrl-w'd the tab and ctrl-shift-T'd it. I've opened the same site in a new tab and it still wouldn't work. I've had to completely shut the browser down. Maybe it's different between Windows and Linux, perhaps (I'm using Windows for this).

Maybe there's more than one cause, but the reason I hate this bug so much is because simple fixes like just alt-tabbing or even closing and re-opening or full-reload doesn't work. I'm like 99% certain that's the case. I'll have to verify next time this happens. It seems to happen at least a couple times a month.